Pneumocystis carinii is an opportunistic organism which is widely prevalent but generally dormant until bodily defenses of the host are compromised whereupon it propagates in the host causing disease. Generally it is present in the lungs although extrapulmonary infections have been reported. Lung infections with this organism in immunocompromised individuals generally lead to pneumonia and are usually fatal if untreated. It has been suggested that patient to patient transmission also may occur in immunocompromised individuals. The immunocompromised state of individuals is usually associated with genetic defects, lymphoproliferative diseases, or with conditions resulting from cancer therapy, or treatment with immunosuppressive drugs, or as a consequence of AIDS. Most AIDS patients eventually contract Pneumocystis carinii pneumonia (PCP) and have accounted for the majority of the recent cases of this disease. Left untreated, PCP is almost always fatal.
The current method of treatment for P. carinii pneumonia is trimethoprim/sulfamethoxazole or pentamidine. Treatment with trimethoprim/sulfamethoxazole (TMP/SMZ) is associated with a high level of toxic side effects including rash, elevated liver function, nausea and vomiting, anemia, creatine elevation, and in extreme cases, Stevens-Johnson syndrome. Side effects from TMP/SMZ are much more prevalent in patients with AIDS. Treatment with pentamidine is also associated with a high level of toxic side effects including renal failure, hepatotoxicity, hypoglycemia, hematologic abnormalities and pain or abscess at the injection site. The mortality due to treatment can reach 20 to 30 percent. An improved method for the treatment of P. carinii pneumonia in immune-compromised patients is greatly needed.